This core will have a critically important role in all 3 projects, providing access to a population of pafients that provide a unique opportunity to develop the techniques and test the instrumentafion that is being developed. One of the potentially limiting factors in the development of accurate and effecfive biodosimetry for triage of large populations potenfially exposed to clinically significant levels of ionizing radiafion has been the lack of suitable samples and subjects to test the validity ofthe assays and to facilitate the development of the techniques. Suitable samples/subjects require exposure to ionizing radiation in the dose range leading to the acute radiation syndrome, (2 -12 Gy). It would be completely unethical to expose human individuals to such doses of radiation for the purpose of developing the methodology and evaluation in animal models is not pracfical or relevant at this stage of development. We can instead, however, utilize pafients who receive such radiafion exposures as part of their treatment for myelosuppression and immunosupression. The DFCI is one ofthe few places in the world where there are large numbers of patients who as a part of their therapy, receive TBI in the dose ranges that are direcfiy pertinent to the levels needed to be measured in the event of a radiafion exposure event. In addition, there are ongoing research programs at DFCI that are invesfigafing the effects of such irradiations and strategies to minimize the effects of the exposures. This provides a unique opportunity to carry out the much-needed development and validafion of a methodology designed to make such measurements as a means of facilitating an effecfive response to an event in which large numbers of people potenfially are exposed to clinically significant dose of ionizing radiafion. The personnel from the DFCI will work with the personnel from the projects to make measurements in the TBI patient populafion in vivo in teeth and nails. Clippings of nails also will be obtained for use by project 2. When the prototype instruments suitable for deployed use by non-expert personnel are constructed, measurements will be made at DFCI using members ofthe team that have not previously been involved with the operafion ofthe instruments, providing a realisfic test ofthe capabilifies ofthe design, with important feedback for improvement of the prototypes.